According to a study by the inventors of the present invention, the following technique with respect to the DR technology is considered. DR is a remote backup system which duplicates information updated in a primary site to a secondary site located in a remote place. As the DR method, there is known a method using a remote copy function of storage. In this method, data written into a storage in the primary site is duplicated to a secondary storage by the remote copy function without using server resources. In the case of a DR system between cities on the assumption of wide area disasters such as an earthquake and the like, it is necessary to connect a primary storage to a secondary storage that is located at a remote place therefrom several hundred kilometers away via a WAN.
In a computer at the primary site, a Database Management System (DBMS) operates. The DBMS refers to or updates data stored in a DB in the storage according to an inquiry from a user Application (AP) on a client. Herein, in the DBMS, in order to realize its performance improvement, updating is carried out on a buffer on a memory, and writing to the storage is carried out at other timing. However, for reliability improvement, with regard to a log as an update difference, writing is made in sync to a log VOL of the storage at the timing of commitment.
In a DR system where sites are several hundred kilometers away from each other, the costs to configure and maintain its line unit (network unit) become high. Especially, in order to maintain a wide-bandwidth line of several hundred kilometers, extremely large costs are required, and in order to reduce the costs, it is necessary to realize the DR by a narrow-bandwidth line. Therefore, there is known a log-based DR method where only logs of the DBMS are transferred, and with regard to a DB main body, duplication is made by applying the logs to the secondary site. In the log-based DR method, in the computer at the secondary site, a log apply unit that reads logs transferred by the remote copy, and applies the read logs to the DB.